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Variable Source Area Hydrology

SWAT Water Balance Model

Hydrology Research Areas:


Variable Source Loading Function (VSLF) Modeling


Example of a precipitation model

Modeling saturated areas of a watershed allow us to understand what parts of the landscape are most likely to produce runoff, and are therefore most vulnerable to pollutant transport. We are hoping to expand a tool that allows farmers to see daily-updated maps of vulnerable areas of their land based on daily precipitation data. This will help them to make management decisions that minimize water pollution from their farms. Models based on the concept of variable source areas may also give us more predictive ability in determining the potential impacts of different best management practices.

Soil and Water Lab people working on this project: Josephine Archibald and Zach Easton (Zach now works at Virginia Tech)

Principal Investigator: Todd Walter



Urban hydrology, biogeochemistry, and function of stormwater infrastructure

As there is development and urbanization of landscapes, we manipulate the natural hydrology. Storm runoff from these impervious surfaces is channeled into various management practices, such as detention basins and road ditches. We have several research projects evaluating the function of these management practices as well as how they influence downstream water quality.

In stormwater detention basins on Cornell's campus, we have been researching how well these basins remove pollutants from incoming runoff. Additionally, we have been assessing whether these basins are acting as sources of greenhouse gases, such as methane and nitrous oxide. For more information on this project check out this webpage

Starting summer 2014, we are beginning a similar project in a suburban watershed in Tompkins County, NY. For this project, we are focusing on how grassed road ditches in this watershed function with respect to impacting downstream water quality, and whether they provide any removal of excess nutrients in stormwater. We will also be assessing whether these ditches serve as hotspots of greenhouse gas emissions by soil microbes, as part of nutrient cycling processes. For more information on this project check out this webpage

We are also tracking transport and impacts of road salt in urban watersheds. Broadly, we're evaluating how long salt is persisting in soils near sidewalks on campus, as well as in the stormwater detention basins. We're also tracking salt export from campus stormwater sewers to nearby Cascadilla Creek as well as monitoring and modeling salt concentrations for Fall Creek. For more information on this project check out this webpage.

Soil and Water Lab people currently working on these projects: Lauren McPhillips, Peri Gerson, Breann Liebermann, Shane DeGaetano

Principal Investigator: Todd Walter

Funding: NYS Water Resources Institute and the Cornell Engineering Learning Initiatives Undergraduate Research Grant Program



Spatially Distributed Travel Time Modeling of Artificial Drainage Networks (finished 2013)

Few hydrologic models simulate both variable source area (VSA) hydrology, and runoff-routing at high enough spatial resolutions to capture fine-scale hydrologic pathways connecting VSAs to the stream network. This research focuses on the development a GIS-based operational model that simulates the spatio-temporal dynamics of VSA runoff generation and distributed runoff-routing, including through complex artificial drainage networks. Application of the model in a nearby agricultural catchment underscores how relatively fine-scale alterations to natural flow pathways can result in substantial impacts to watershed scale hydrology and water quality and may help to inform spatially-targeted water resource management decisions and future modeling efforts.

Soil and Water Lab people working on this project: Brian Buchanan



Mapping Hydrologically Sensitive Areas in the Upper Susquehanna River Basin (finished 2013)

A Hydrologically Sensitive Area (HSA) is any area in a watershed that is prone to generating runoff and therefore has the potential to transport pollutants. This is a concept derived from Variable Source Area (VSA) hydrology. Since HSAs can be small portions of a watershed that account for a disproportionate large amount of overland flow, it is necessary to predict the runoff risk and location of HSAs. One of the projects in the soil and water lab is quantifying the risk of soil saturation and mapping HSAs in the Upper Susquehanna Watershed in a Geographic Information System (GIS) to help water quality protection.


GIS Map of the Upper Susquehanna Watershed


We use a modified Soil Conservation Service curve number (SCS-CN) method to estimate runoff risk as well as the fraction of runoff generating areas and its corresponding frequency. Considering the geography of the Northeastern USA, we treat the production of runoff as a bivariate process which involves the interaction between precipitation and precedent soil moisture conditions. Based on the predicted spatial extent of saturated areas, runoff generating areas are mapped in a Geographic Information System (GIS) using a Soil Topographic Index (Walter et al. 2002. Hydrological Processes 16(10): 2041-2046) throughout the watershed.

Soil and Water Lab people working on this project: Xiaoya Cheng